Sample identification by measurement of wavelength of luminescence utilizing plasma discharge lamp excitation and continuous interference filter

ABSTRACT

In an apparatus for detecting the intensity of luminescence at various wavelengths emitted by a sample under test, the sample is excited by light from a plasma discharge flash lamp coupled to an electrical supply circuit including means for storing electrical energy and repeatedly discharging rapidly the stored energy to produce flashes of high peak intensity over a continuous range of wavelengths in the exciting wavelength region. A continuous interference filter is movable across the path of luminescence from the sample to a detector for analysing the wavelength of luminescence emittal.

lwZz -W r XR 367873 United States Patent [1 1 [111 3,787,695 West Jan.22, 1974 SAMPLE IDENTIFICATION BY 3,205,767 A 9/1965 Weber et a1.350/314 x MEASUREMENT OF WAVELENGTH OF 3,666,945 5/1972 Frungel et a]250/83.3 UV X R25,320 1/1963 Lewis et a1 250/71 G X LUMINESCENCEUTILIZING PLASMA 3,433,952 3/1969 Howerton DISCHARGE LAMP EXCITATION AND3,449,571 6/1969 Hoerman et a1. 250/71 G CONTINUOUS INTERFERENCE FILTER3,497,690 2/1970 Wheeless, Jr. et al. 250/83.3 UV X [75] Inventor:Michael Anthony West, Orpington,

England Primary Examiner-Archie R. Borchelt [73] Assignee: The RoyalInstitution of Great Attorney Agent Firm peter Smolka et Britain,London, England [22] Filed: Sept. 15,1971

[57] ABSTRACT [21] Appl, No.: 180,628

In an apparatus for detecting the intensity of luminescence at variouswavelengths emitted by a sample [30] Forelgn Apphcatlmi P rlomy Dataunder test, the sample is excited by light from a Sept. 17, 1970 GreatBritain 44524/70 plasma discharge flash lamp coupled to an electricalsupply circuit including means for storing electrical [52] US. Cl250/365, 250/301, 250/504, energy and repeatedly discharging rapidly thestored 350/314 energy to produce flashes of high peak intensity over a[51] IIPK. Cl. G01 23/00 continuous range of wavelengths in the excitingwave [58] Field of Search... 250/71 G, 77, 83.3 UV, 365,

length region. A continuous interference filter is mov- 2 504; 350/314318 able across the path of luminescence from the sample to a detectorfor analysing the wavelength of 1umines [56] References Cited cenceemittah UNlT ED STATES PATENTS 2,590,080 3/1952 Adams 350/314 X 10Claims, 6 Drawing Figures RECORDER PATENTED JAN 2 21974 SHEET 1 0r 4PATENTEB JAN 2 2 i974 SHEET 2 OF 4 Wave/engfh PATEHTED JAN 2 2 I974SHEET 3 BF 4 0.0. SOURCE 3 65 A.C. SOURCE MOTOR PATENTED 3,787, 695

SHEET 4 OF 4 [0g Lg} 84 G Dev/re J 8/ I 20 A 0y Heron/er 3'0 021002SAMPLE IDENTIFICATION BY MEASUREMENT OF WAVELENGTH OF LUMINESCENCEUTILIZING PLASMA DISCHARGE LAMP EXCITATION AND CONTINUOUS INTERFERENCEFILTER BACKGROUND OF THE INVENTION This invention relates to apparatusfor detecting in terms of wavelength the luminescence emitted by samplespecimens, including the measurement of fluorescence in all samplephases or phosphorescence in solid sample phases.

In known apparatus for measuring fluorescence in samples of materialsunder test, the light sources used for exciting the samples haveincluded quartz iodine direct current filament lamps. However theselamps lack the light intensity required in the ultra violet region forexcitation in modern analysis of samples of materials. Low pressure gasdischarge lamps have been used but these are characterised by a linespectrumwhich is generally unsuitable for exciting unknown samples. Arclamps have a continuous spectrum and provide sufficient intensity in theultra violet region but they are expensive, and occupy a large space.Known apparatus may incorporate broad band colour filters through whichthe light from the illuminated specimen passes, but they only give anindication of the amount of light emitted over a wide spectral range bythe sample specimens of materials and do not give the spectralresolution required. Monochromators have been used to achieve therequired resolution but they are large and expensive.

The main object of the present invention is to provide apparatus foranalysing samples of materials in which the aforesaid disadvantages ofinsensitivity and lack of spectral resolution are minimised oreliminated.

SUMMARY OF THE INVENTION The present invention provides apparatus fordetecting the intensity of luminescence at various wavelengths emittedby a sample under test, comprising a support for a sample under test, aplasma discharge flash lamp coupled to an electrical supply circuitincluding means for storing electrical energy and repeatedly dischargingrapidly the stored energy to produce flashes of high peak intensity overa continuous range of wavelengths in a required wave length region,means for confining a beam of light from the lamp towards the sampleunder test, a light detector arranged to detect luminescence emittedfrom the sample and not the rays illuminating the sample and provideanelectrical output signal dependent on the intensity of luminescencedetected, and a continuous interference filter device located betweenthe light detector and the sample, together with means for restrictingthe path width of luminescence incident on the filter, the filter devicebeing movable across the path of luminescence so as to vary thewavelength which may be transmitted from the sample to the detector.

By plasma discharge flash lamp is meant a lamp having an envelope atleast part of which is transparent, containing the gas through which thedischarge occurs to produce the flash. The plasma discharge lamp isconstituted and operationally arranged for energisation by the suddenrelease of high peak electrical energy, the object being to elevate thetemperature of the plasma to a level at which high peak light flasheshaving a substantially continuous spectrum are generated.

It is necessary for the lamp to provide a substantial output intensityover a continuous range of wavelengths in'an appropriate spectralregion. When an unknown sample is tested in an apparatus embodying thepresent invention, the necessary wavelength needed to excite the samplewill not be known in advance and consequently it is necessary for thelamp to emit a continuous spectrum rather than a line spectrum, coveringa range of wavelengths within which the unknown excitation wavelength orwavelengths, is or are likely to lie.

A particularly suitable excitation range is 200 nanometers to 400nanometers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows diagrammatically anapparatus for use in measuring in terms of wavelength the colour of atest specimen extressing the measuring by three possible devices,namely, a meter, a chart recorder and an oscillograph; 1

FIG. 2 shows diagrammatically a continuous'spectral colour filter foruse in the apparatus of FIG. 1;

FIG. 3 shows the output spectrum of a light source used in oneembodiment of the present invention;

FIG. 4 shows in more detail the electrical circuit used for operatingthe light source in FIG. 1;

FIG. 5 shows an arrangement for compensating for variations in theoutput intensity of the light source used in FIG. 1; and

FIG. 6 shows a device which may be used with apparatus of the type shownin FIG. 1 to compensate for any non linearity in the wavelengthtransmission of the filter used.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, theapparatus of FIG. 1 has a gas filled plasma discharge flash lamp 1 ofconventional construction energised by pulsed direct electric currentthrough a capacitor 2 connected to terminals 3. The lamp may be filledwith an inert gas, e.g.,

xenon, argon or krypton, or a mixture of inert and other gas, e.g.,hydrogen. The lamp 1 is shown as U- shape but it may be a single turncoil tube or have several coils or be of other suitable construction,the lamp being operated by discharge of electricity sto'red'in thecapacitor 2 which is rapidly recharged from a DC. power supply, thefrequency of the-lamp flashes depending on the supply of electronicpulses to a capacitor 5 through a trigger coil 4 to trigger the lamp.The direct current supply can be of any conventional type.

The lamp 1 is housed in a casing 6 through which the current leads 7pass through grommets or like means which do not permit light to pass.The lamp casing is cooled by a conventional fan 8 in a housing 9 drivenfor example by an electric motor 10 suppliedby current through leads 11.

The housing 6 has an inlet opening 12 from the fan 8 and an outlet oroutlets for the circulating air may be slits (not shown) in the housingin the conventional manner. The housing 6 has an aperture 13, of anyshape but preferably a vertical slit three-fourths inch wide and 1% to 2inches high through which a beam of light,'indicated by an arrow 14,from the lamp passes.

A mirror is provided to direct light towards the aperture 13. A lens 16is shown in the path of the light rays from the lamp to concentratethelight on the sample under test.

In the path of this beam between the lamp 1 and the specimen to bedescribed is an ultraviolet light filter 19 of conventional form such asfor example an OX7 or OX9 filter manufactured by Chance-PilkingtonLimited. This filter is shown on the outside of the housing 6 but it maybe in the housing 1. The pulsating filtered light beam 17 from theaperture is directed in the direction shown by the arrow marked 17.

The light source used in FIG. 1 may comprise a 200 Joule xenon filledflash lamp capable of being fired between 96 and 3,600 flashes perminute. One example of a suitable flash lamp is type MF'T-lSlMmanufactured by Elevam Company of Japan. The lamp is preferably operatedat at least 2,000 flashes per minute and at such a level of energisationso that the sample is illuminated by a very rapid succession of shortduration flashes having high peak intensity. The output wavelengthcharacteristic of the light from the source is shown by the curve 50 inFIG. 3. As is shown, the lamp provides a substantial output intensityover a continuous range of wavelengths from about 300 nanometers up toabout 600 nanometers. This provides a substantial intensity over theultra violet range of 300 to 400 nanometers. When the filter 19 shown inFIG. 1 is an OX9 filter, the wavelength/intensity curve for the lighttransmitted to the sample is shown by the curve 51 in FIG. 3. Thispermits transmission of light from the lamp in the range 300 to 400nanometers.

The electrical circuit for operating the lamp in FIG. 1 is shown in moredetail in FIG. 4 and the same reference numerals have been used as inFIG. 1. The terminals 3 are connected to a 500 volt D.C. source 63. AnA.C. source 53 drives the motor 10 and feeds a transformer 54 having asecondary winding 56. The winding 56 charges a capacitor 57 through adiode 58. A Zener diode 59 is connected across the capacitor 57 andbreaks down when the voltage on the capacitor 57 reaches a predeterminedvalue. When the Zener diode 59 breaks down, this switches unijunctiontransistor 60 which in turn operates a thyristor 61. The thyristorcontrols discharging of the capacitor 5 which thereby provides pulses onthe trigger coil 4 of the lamp 1 in order to control the frequency offlashning of the lamp 1.

In the path of the beam 17 is a specimen holder 20. In this example thespecimen 94 is an elongated rectangular piece of PERSPEX in which thesample in solid phase'of the material to be tested is dispersedpreferably homogeneously. Other shapes may be used and any suitableholder such as a quartz cell may be used if the specimen is a gas or aliquid. The holder is in the form of a base fixed to the framesupporting the whole apparatus with upstanding walls into which thespecimen is a sliding fi't to locate it firmly so that the major portionof its length is above the holder in the light beam 17. Thus when thelamp 1 is energised the pulsed beam 17 impinges on the specimen in theholder and the specimen emits luminescence characteristic of thespecimen: for example a light blue for anthracene, green for ovalene ororange red for rhodamine B and so on.

Attached to the holder is a closed duct or tunnel 21 the other end ofwhich is light-excludingly sealed to the casing 22 at an aperture 22atherein. The casing houses a light detector in the form of aphotomultiplier 24.

The photomultiplier is' of conventional construction and has alight-detecting photocathode 25 in an envelope 24 which is responsive tothe light directed onto it from the specimen 5. Depending on thecharacteristic specimen light emission and the spectral response of forexample vertical strips 2 mm wide.

A continuous interference filter 34 (which may for example be a type S60manufactured by Jenaer Glaswerk Schott) is mounted in the space betweenthe wall 18 and the apertured outer casing wall 18a and has a toothedrack 36 (FIG. 2) on its underside meshing with a gear driven throughmeshing gears 26 mounted in bearings fixed with respect to the casing,the lower gear in FIG 1 being driven as by the motor 26a also fixed withrespect to the casing. By energising the motor the filter can be movedacross .the apertures 22a, 23 between fixed micro-switches 26b which ateach end of the filter movement operate to break the motor circuit. Itcan thus be moved back and forth under control of the operator. Thefilter 34 (FIG. 2) is a plate transparent at predetermined wavelengthse.g. glass or quartz mounted in a frame with the toothed rack and has ahorizontal linear scale 37 showing the distance the filter has traversedfrom one of its ends across the specimen light-rays. The plate hasvertical colour bands 38 of the spectrum and these changes from one toanother colour across the plate as in a natural spectrum. As the filtertraverses the specimen light rays the filtered light reaching the device25 will change in wavelength and when the colour which is characteristicof the wavelength of the luminescence emitted corresponds with thewavelength transmitted by the filter 33 the maximum output signal willbe emitted by the device 28 giving the peak 29 in the graph as shown forthe oscillograph 28 of FIG. 1 and corresponding to the known wavelengthsdependent on the particular filter employed. The two slits 22a and 23are aligned on opposite sides of the filter and limit the path width ofthe luminescence transmitted through the filter.

The filter plate 33 has clear end bands 39, 40 which at clearly definedinstants allow all light rays from the specimen to pass so that there isa graph between accurately defined linear points 41 and 42 at the endsof the scale 37 and thus from this scale the wavelength of the specimenlight rays is displayed directly.

The signal from the photomultiplier may be transmitted to a suitablemeter 27 which due to its response time does not show fluctuation due toflashing of the light source. The meter indicates the luminescenceintensity at a particular wavelength. Alternatively the signal may betransmitted to a suitable conventional chart recorder 30 having forexample a rotary drum with a roll of chart paper thereon and a styluswhich produces a typical graphical representation of the signal in anydesired manner indicative of the wavelength of the light. Anotherrecording device is shown as the oscillograph 28. On this oscillographthe curve of filter displacement against luminescence is recorded andthis has a peak 29 where the wavelength of the luminescence of thespecimen corresponds to the wavelength transmitted by the filter.

The lamp 1 provides a substantially constant output intensity with time.However, some fluctuations may occur and means may be provided to avoiderroneous output signals being fed to the recorder 30 in this case. FIG.5 shows such an arrangement. A second light detector 80, which may besimilar to the photomultiplier 24, is positioned to receive light alonga path 81 from the lamp 1. An adjustable attenuator 82 is provided inthe path 81 so as to achieve a suitable output signal level from thedetector 80. The output from detector 80 is fed along line 83 to a unit84 which provides on output line 85 a signal representing the logarithmof the output from the detector 80. Similarly the output of the detector24 is fed to a unit 86 which provides on line 87 a signal representingthe logarithm of the output from the detector 24. The two lines 85 and87 provide inputs to a difference unit 88 which feeds along line 89 asignal proportional to the difference of the two input signals. Line 89is connected to device 90 which provides on the output line 91 theantilog of the signal on line 89. This antilog signal is proportional tothe ratio of the two signals from the detectors 80 and 24 and is fed tothe recorder 30. In this way,the signal recorded by the recorder isindependent of fluctuations in the output intensity of the lamp 1.

The continuous interference filter 33 which is used may have a variationof transmitted wavelength from about 390 nanometers to 700 nanometers.As earlier noted the plate has vertical colour bands 38 of the spectrumand these change from one to another colour across the plate as in anatural spectrum. It will thus be appreciated that the filter provides astepless variation in wavelength transmission. As such, the filterprovides for wavelength selectivity enabling analysis of the intensityof emitted radiation at different wavelengths.

The wavelength variation along the length of the filter is preferablysubstantially linear. There are however difficulties in making suchfilters with accurate linearity along their length. Any non linearitymay however be compensated by providing avariable drive coupling betweenthe filter and the motor arranged to drive it. Such an arrangement isshown in FlG. 6. In this case, the filter 33 is connected by a rod 72 toa rotatable cam 71. The periphery of the cam 71 is frictionally engagedby a wheel 70 driven by the gear wheel 26, in FIG. 1. The'cam 71 ispivotally mounted on a pin 73 slidable in a slot 74 in the cam 71.Theperiphery of the cam 71 is so shaped as to alter the speed ofmovement of the filter 33 as the wheel 70 rotates and thereby compensatefor any non linearity in the filter 33. In the arrangement shown in FIG.6, the filter is arranged to slide horizontally between upper and lowerchannel members 92 and 93 and the rack 36 shown in FIG. 2 is notprovided.

A wavelength dial may be provided on the circular face of one of thegears 26 while a fixed datum point is provided adjacent the dial toindicate the particular colour of wavelength band in the path of thelight passing the apertures 22a, 23.

The ultraviolet filter 19 may itself be a continuous interference filtercovering a range of ultraviolet wavelengths so that the ultravioletwavelengths used to illuminate the specimen under test may be varied byadjustment of the position of the filter relative to the beam 17.

It can thus be seen that by means of the invention the luminescence ofthe specimen can be analysed quickly and automatically with a simpleapparatus which is convenient to operate, is small in size andinexpensive to make. Various characteristicsof the luminescence can bemeasured for example the fluorescence by the wavelength of the specimenlight rays and the phosphorescence by the duration of the colourationafter the lamp ll has been switched off. It is possible for all suchdata to be recorded on the one graph thus giving rapid analysis of thedesired characteristics of the specimen as well as the material of thespecimen itself.

It will be appreciated that by using a pulsed light source it ispossible to achieve very high intensity of illumination of the sample atthe peaks of the illumination. As the peaks are of only short duration,the samples are not harmed by the high level ofillumination. On theother hand, the peak illumination is of sufficient intensity to achievethe accurate results even with specimens which are weakly luminescent.Furthermore, the use of a continuous interference filter to analyse thelight emitted by the sample under test enables good spectral resolutionto be achieved from the output signals of the photomultiplier 24. v

I claim:

1'. Apparatus for identifying in terms of an electrical output thewavelength of the luminescence emitted by a luminescent sample underexciting radiation by analysing the intensity of emitted radiation atdifferent wavelengths, said apparatus comprising a sample stationwhereat a sample may be supported at a predetermined location, a plasmadischarge flash lamp for producing exciting radiation flashes of highpeak intensity over a continuous range of wavelengths in a luminescenceexciting region, an electrical supply circuit including a capacitor forstoring electrical energy and discharging through said lamp with a highrepetition rate, means for defining the path boundary of a beam of lightdirected in operation from the lamp to the sample under test, atransducer arranged to receive the luminescence emitted from the samplein adirection not included in said boundary at the substantial exclusionof direct rays from the lamp, said transducer being capable of providingan electrical output related to the intensity of the luminescencefalling thereon, and a continuous filtering arrangement includingwavelength selective interference filter means, providing over its areaa stepless variation in wavelength transmission over a predeterminedrange and mounted for movement past the transducer, for varying thewavelength of said luminescence to enable said transducer to provide anelectrical output related to intensity of said luminescence at differentwavelengths, said filter means enabling the wavelength of theluminescence to be identified in terms of the electrical output of thetransducer as the successive portions of the continuous filtercorresponding to successive wavelengths in said predetermined range arescanned past the transducer.

2. Apparatus for detecting the intensity of luminescence at variouswavelengths emitted by sample under test, which apparatus comprises asupport for a sample under test, a plasma discharge flash lamp coupledto an electrical supply circuit including means for alternately storingand discharging rapidly stored electrical energy to produce flashes ofhigh peak intensity over a continuous range of wavelengths in a requiredwavelength region, means for confining a beam of light from the lamptowards the sample under test, a light detector arranged to detectluminescence emitted from the sample luminescence detected, and acontinuous interference filter device located between'the light detectorand the sample, the filter device including wavelengthselective filterplate means with stepless variation in wavelength transmission togetherwith means for restricting the path width of luminescence transmitted bythe filter, said filter plate means being movable across the path ofluminescence so as to vary the wavelength which may be transmitted fromthe sample to the detector to enable said light detector to detect theintensity of said luminescence at different wavelengths.

3. Apparatus as claimed in claim 2, in which the lamp is arranged toprovide a continuous spectrum in the range of at least 200 to 400nanometers.

4. Apparatus as claimed in claim 2, in which the lamp is filled withinert gas.

5. Apparatus as claimed in claim 2, in which the continuous interferencefilter device plate means has an approximately linear varation ofwavelength transmission along its length.

6. Apparatus as claimed in claim 5, including a constant speed motor formoving the filter.

7. Apparatus as claimed in claim 6, including a variable mechanicallinkage, generating a linearising mechanical function, connected betweenthe filter and the motor.

8. Apparatus as claimed in claim 2, in which means is provided forcompensating for any fluctuations in the output intensity of the flashlamp.

9. Apparatus as claimed in claim 8, in which a second light detector isarranged to detect light from the lamp and provide an electrical signaldependent on the output intensity, means also being provided to receivethe electrical output signals from the two light detectors and provide asignal representing the ratio of the two signals.

10. Apparatus as claimed in claim 2, in which the light detector isarranged to sense luminescence emitted from the sample in a directionsubstantially normal to the direction of the beam from the lamp to thesample.

1. Apparatus for identifying in terms of an electrical output thewavelength of the luminescence emitted by a luminescent sample underexciting radiation by analysing the intensity of emitted radiation atdifferent wavelengths, said apparatus comprising a sample stationwhereat a sample may be suppOrted at a predetermined location, a plasmadischarge flash lamp for producing exciting radiation flashes of highpeak intensity over a continuous range of wavelengths in a luminescenceexciting region, an electrical supply circuit including a capacitor forstoring electrical energy and discharging through said lamp with a highrepetition rate, means for defining the path boundary of a beam of lightdirected in operation from the lamp to the sample under test, atransducer arranged to receive the luminescence emitted from the samplein a direction not included in said boundary at the substantialexclusion of direct rays from the lamp, said transducer being capable ofproviding an electrical output related to the intensity of theluminescence falling thereon, and a continuous filtering arrangementincluding wavelength selective interference filter means, providing overits area a stepless variation in wavelength transmission over apredetermined range and mounted for movement past the transducer, forvarying the wavelength of said luminescence to enable said transducer toprovide an electrical output related to intensity of said luminescenceat different wavelengths, said filter means enabling the wavelength ofthe luminescence to be identified in terms of the electrical output ofthe transducer as the successive portions of the continuous filtercorresponding to successive wavelengths in said pre-determined range arescanned past the transducer.
 2. Apparatus for detecting the intensity ofluminescence at various wavelengths emitted by sample under test, whichapparatus comprises a support for a sample under test, a plasmadischarge flash lamp coupled to an electrical supply circuit includingmeans for alternately storing and discharging rapidly stored electricalenergy to produce flashes of high peak intensity over a continuous rangeof wavelengths in a required wavelength region, means for confining abeam of light from the lamp towards the sample under test, a lightdetector arranged to detect luminescence emitted from the sample and notthe rays illuminating the sample and provide an electrical output signaldependent on the intensity of luminescence detected, and a continuousinterference filter device located between the light detector and thesample, the filter device including wavelength selective filter platemeans with stepless variation in wavelength transmission together withmeans for restricting the path width of luminescence transmitted by thefilter, said filter plate means being movable across the path ofluminescence so as to vary the wavelength which may be transmitted fromthe sample to the detector to enable said light detector to detect theintensity of said luminescence at different wavelengths.
 3. Apparatus asclaimed in claim 2, in which the lamp is arranged to provide acontinuous spectrum in the range of at least 200 to 400 nanometers. 4.Apparatus as claimed in claim 2, in which the lamp is filled with inertgas.
 5. Apparatus as claimed in claim 2, in which the continuousinterference filter device plate means has an approximately linearvaration of wavelength transmission along its length.
 6. Apparatus asclaimed in claim 5, including a constant speed motor for moving thefilter.
 7. Apparatus as claimed in claim 6, including a variablemechanical linkage, generating a linearising mechanical function,connected between the filter and the motor.
 8. Apparatus as claimed inclaim 2, in which means is provided for compensating for anyfluctuations in the output intensity of the flash lamp.
 9. Apparatus asclaimed in claim 8, in which a second light detector is arranged todetect light from the lamp and provide an electrical signal dependent onthe output intensity, means also being provided to receive theelectrical output signals from the two light detectors and provide asignal representing the ratio of the two signals.
 10. Apparatus asclaimed in claim 2, in which the light detector is arranged to senseLuminescence emitted from the sample in a direction substantially normalto the direction of the beam from the lamp to the sample.